Check your receiving address out on blockchain.info. The probability is high that there is an advertising text in the comment field, advertising some scam site or so.
Spot on:
Public Note: MAKE 1 BTC DAILY MINING FROM YOUR OWN PC WITH NO SPECIAL HARDWARE OR MINING RIGS NEEDED! FARM YOUR FUTURE AT X-BITCOINS.COM !
This kind of spam is relatively common unfortunately.
I've gotten spam dust like this before but usually the amount is less in value. Must be the lower price that makes it affordable to spam this way ;-)